TSV formation processes using TSV-last approach

ABSTRACT

A device includes a semiconductor substrate having a front surface and a back surface opposite the front surface. An insulation region extends from the front surface into the semiconductor substrate. An inter-layer dielectric (ILD) is over the insulation region. A landing pad extends from a top surface of the ILD into the insulation region. A through-substrate via (TSV) extends from the back surface of the semiconductor substrate to the landing pad.

This application is a continuation of and claims benefit of U.S. patentapplication Ser. No. 12/834,304, filed Jul. 12, 2010, entitled “TSVFormation Processes Using TSV-Last Approach,” which application ishereby incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates generally to interconnection structures, andmore particularly to structures and manufacturing methods of TSVs.

BACKGROUND

Among the efforts to increase device density in integrated circuits,three-dimensional integrated circuits (3DICs) are commonly used.Through-substrate vias (TSV) are often used in 3DIC for connectingmultiple dies to package substrates. There are several commonly usedapproaches for forming TSVs. For example, TSVs may be formed beforeinter-layer dielectric (ILD) is formed (which approach is referred to asa via-first approach), or formed after the formation of ILD and beforethe formation of the bottom metal layer (M1, which approach is referredto as a via-middle approach). TSVs may also be formed after all metallayers and passivation layers are formed, and may be formed from thefront side or the back side of the respective wafers/chips, whichapproaches are referred to as via-last approaches.

In the manufacturing of TSVs using the via-last approach, wherein theTSVs are formed from the backside of a wafer, an etch needs to beperformed to etch through a semiconductor substrate, shallow-trenchisolation (STI) pads, and an inter-layer dielectric over the STI pads,so that the metal pads in a bottom metal layer are exposed through therespective TSV openings. However, serious lateral etching may occur inthe ILD, causing the portions of the TSV openings in the ILD to be widerthan the portions of the TSV openings in the semiconductor substrate.This results in difficulty in the formation of isolation layers, whichare formed on the sidewall of the TSV openings. Further, during theformation of the TSV openings, the metal pads in the bottom metal layermay be undesirably etched. Since the metal pads are very thin, they mayalso be etched through.

SUMMARY

In accordance with one aspect, a device includes a semiconductorsubstrate having a front surface and a back surface opposite the frontsurface. An insulation region extends from the front surface into thesemiconductor substrate. An inter-layer dielectric (ILD) is over theinsulation region. A landing pad extends from a top surface of the ILDinto the insulation region. A through-substrate via (TSV) extends fromthe back surface of the semiconductor substrate to the M0 metal pad.

Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1 through 8B are cross-sectional views of intermediate stages inthe manufacturing of a TSV in accordance with an embodiment; and

FIG. 8C illustrates a top view of the embodiments shown in FIGS. 8A and8B.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

A novel through-substrate via (TSV) and the methods of forming the sameare provided. The intermediate stages of manufacturing an embodiment areillustrated. The variations of the embodiment are discussed. Throughoutthe various views and illustrative embodiments, like reference numbersare used to designate like elements.

Referring to FIG. 1, wafer 2, which comprises substrate 20, is provided.Substrate 20 may be a silicon substrate, or may be formed of othercommonly used semiconductor materials. In addition, substrate 20 may bein the form of a bulk semiconductor. Integrated circuits 22, which aresymbolized using a transistor, may be formed at the surface of substrate20. Substrate 20 includes front surface 20 a and back surface 20 b.

Shallow trench isolation (STI) regions 24 and 25 are formed in substrate20, for example, by forming shallow trenches in substrate 20, and thenfilling the trenches with a dielectric material. STI regions 24 may alsobe referred to as STI pads 24. An exemplary dielectric material includeshigh-density plasma (HDP) silicon oxide. In an embodiment, STI pads 24are formed simultaneously with the formation of STI regions 25, whichare used for isolating active devices such as transistors.Alternatively, STI pads 24 and STI regions 25 are separately formed sothat STI regions 24 may have an optimized thickness different from thethickness of STI regions 25.

Referring again to FIG. 1, an etch stop layer (ESL, not shown) may beblanket formed over integrated circuits 22, substrate 20, and STIregions 24 and 25. Inter-layer dielectric (ILD) 32 is then formed overthe ESL. ILD 32 may be formed of phospho-silicate glass (PSG),boron-phospho-silicate glass (BPSG), or the like. Gate contact plugs andsource/drain contact plugs 34, which may be formed of tungsten, may thenbe formed in ILD 32 and electrically coupled to integrated circuits 22.As shown in FIG. 1, contact plugs 34 (including gate contact plugs andsource/drain contact plugs) are coupled to source and drain regions 22A,and gate electrode 22B of a transistor.

Referring to FIGS. 2A and 2B, TSV landing pads 38 (referred to as M0metal pads 38 hereinafter) are formed. M0 metal pads 38 are such namedsince they are under the subsequently formed bottom metal layer that iscommonly known as M1, as illustrated as 40 in FIG. 3. M0 metal pads 38are formed by etching ILD 32 and STI pads 24 to form openings, andfilling metallic materials into the openings. In an embodiment as shownin FIG. 2A, STI regions 24 are not etched through, and the etching isstopped at an intermediate level between top surfaces 24 a and bottomsurfaces 24 b of STI regions 24. Accordingly, the bottom surfaces of M0metal pads 38 are between surfaces 24 a and 24 b of STI pads 24. Each ofM0 metal pads 38 may include conductive barrier layer 38A and innerregion 38B. Barrier layer 38A may be formed of titanium, titaniumnitride, tantalum, tantalum nitride, or the like, while inner region 38Bmay be formed of copper or copper alloys. In an exemplary embodiment,the portions of M0 metal pads 38 inside STI pads 24 have thickness T1,which may be greater than about 10 percent, or even greater than about30 percent, thickness T2 of STI pads 24. The sidewalls of M0 metal pads38 may be substantially straight.

In alternative embodiments as shown in FIG. 2B, the openings for M0metal pads 38 extend to level with, or lower than (as shown with dottedlines), bottom surfaces 24 b of STI pads 24. Accordingly, dielectricliners 38C are formed, wherein barrier layer 38A may be formed ondielectric liners 38C, followed by the formation of inner region 38B. Inan exemplary embodiment, M0 metal pads 38 may extend below bottomsurfaces 24 b of STI pads 24 by distance D greater than about 5 percent,or even greater than about 10 percent, thickness T2 of STI pads 24.

Next, as shown in FIG. 3, bottom metal layer 40 is formed, and includesdielectric layer 42 (commonly known as an inter-metal dielectric (IMD)),and metal pads 44A and metal lines 44B in dielectric layer 42. IMD 42and overlying IMDs that are formed in subsequent process steps may beformed of low-k dielectric materials. M1 pads 44A contact M0 metal pads38, and may have a top view shape the same as the top view shape of therespective underlying M0 metal pads 38. Further, metal lines 44B areconnected to contact plugs 34.

In subsequent steps, as shown in FIG. 4, additional metal layers (notmarked) are formed, followed by the formation of passivation layers (notmarked) and metal bumps 48. The formation of the front-side structuresof the respective wafer 2 is thus finished. The details of formationprocesses are known in the art, and thus are not discussed herein.

Referring to FIG. 5, carrier 50 is bonded to the front side of wafer 2.The backside of substrate 20 is grinded, until the thickness ofsubstrate 20 is reduced to a level suitable for forming TSVs. Next, asshown in FIG. 6, TSV openings 52 are formed by etching substrate 20 fromback surface 20 b. In the embodiments wherein M0 metal pads 38 have thestructure as shown in FIG. 2A, an additional etching step is performedto etch the portions of STI pads 24 that are directly underlying M0metal pads 38 (please refer to FIG. 8B, wherein the TSV openings arefilled with TSVs 60 and isolation layers 56). M0 metal pads 38 are thusexposed through TSV opening 52. In the embodiments wherein M0 metal pads38 have the structure as shown in FIG. 2B, dielectric liner 38C is alsoetched, as shown in FIG. 6. Further, openings 52 may penetrate throughbarrier layer 38A and stop on inner region 38B, or stop on barrier layer38A.

Referring to FIG. 7, isolation layer 56 is formed in TSV openings 52 andon sidewalls of substrate 20, which sidewalls are exposed to TSVopenings 52. Isolation layer 56 may be formed of silicon nitride,silicon oxide, or the like, although other commonly used dielectricmaterials may be used. Next, the bottom portions of isolation layer 56are removed, for example, using a dry etch. M0 metal pads 38 are thusexposed again.

In FIG. 8A, TSVs 60 are formed. An exemplary formation process of TSVs60 includes forming a barrier layer (not shown), a seed layer (notshown) on the barrier layer, and then performing an electro-chemicalplating (ECP) to fill the remaining portions of TSV openings 52 with ametallic material such as copper. The barrier layer may be formed oftitanium, titanium nitride, tantalum, tantalum nitride, or the like. Theseed layer may be formed copper. A planarization step may be performedto remove excess portions of the barrier layer, the seed layer, and thefilling material outside TSV openings 52. The remaining portions areTSVs 60. In a subsequent step, carrier 50 is de-bonded from wafer 2.

FIG. 8B illustrates the structure formed from the structure shown inFIG. 2A. In this embodiment, it is observed that TSVs 60 extend overbottom surfaces 24 b of STI pads 24, and extend into lower portions ofthe respective STI pads 24. Depending on where TSV openings 52 stop,TSVs 60 may contact a bottom surface of barrier layer 38A (please referto FIG. 6), or penetrate through barrier layer 38A to contact innerregion 38B.

FIG. 8C illustrates a top view of the structure as shown in FIGS. 8A and11B, wherein the top view is obtained from planes crossing lines 11C-11Cin FIGS. 8A and 11B. In the top view, STI pads 24 may have a roundshape, a rectangular shape, or any other polygon shape such as a hexagonshape or an octagon shape. TSVs 60 and M0 metal pad 38 may also haveshapes similar to each other. Further, TSVs 60 contact center regions ofthe respective M0 metal pads 38.

With the formation of M0 metal pads 38, and TSVs 60 that land on M0metal pads 38, the process window is significantly increased. Due to thegreat thickness of M0 metal pads 38, there will be no damage to M1 metalpads 44A during the formation of TSVs 60. Accordingly, TSVs 60 may bereliably coupled to M1 pads 44A.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A circuit structure comprising: a semiconductorsubstrate; a shallow trench isolation (STI) region extending from a topsurface of the semiconductor substrate into the semiconductor substrate;a metal pad extending from a top surface of the STI region into the STIregion, wherein the metal pad is encircled by the STI region, with anedge of the metal pad being in contact with an inner edge of the STIregion to form an interface; and a through-substrate via (TSV) extendingfrom a back surface of the semiconductor substrate to contact a firstportion of a bottom surface of the metal pad, with a second portion ofthe bottom surface of the metal pad extending beyond edges of the TSV.2. The circuit structure of claim 1 further comprising: an inter-layerdielectric (ILD) over the STI region, wherein the metal pad furtherextends into the ILD.
 3. The circuit structure of claim 1, wherein theinterface is lower than the top surface of the semiconductor substrate.4. The circuit structure of claim 1, wherein a bottom surface of themetal pad is between the top surface and a bottom surface of the STIregion, and wherein the TSV penetrates through a lower portion of theSTI region to contact the metal pad.
 5. The circuit structure of claim1, wherein a top surface of the STI region is lower than a top surfaceof the metal pad.
 6. The circuit structure of claim 1, wherein theinterface extends from the top surface of the semiconductor substrateinto the semiconductor substrate.
 7. The circuit structure of claim 1,wherein the bottom surface of the STI region is at an intermediate levelbetween the top surface and the back surface of the semiconductorsubstrate.
 8. The circuit structure of claim 1, wherein the STI regionhas substantially vertical sidewalls extending to an intermediate levelbetween the top surface and the back surface of the semiconductorsubstrate.
 9. The circuit structure of claim 8, wherein the STI regionextends beyond a sidewall of the metal pad outwardly for a firstthickness, and the STI region extends deeper than the metal pad by asecond thickness, and the first thickness is greater than the secondthickness.
 10. A circuit structure comprising: a semiconductorsubstrate; a shallow trench isolation (STI) region extending from a topsurface of the semiconductor substrate into the semiconductor substrate;a metal pad extending from a level higher than a top surface of the STIregion into a center portion the STI region, with an outer portion ofthe STI region forming a ring encircling the metal pad, wherein theouter portion comprises an inner edge in physical contact an edge of themetal pad to form an interface, and the interface forms a full ring; anda through-substrate via (TSV) extending from a back surface of thesemiconductor substrate to contact a bottom surface of the metal pad.11. The circuit structure of claim 10 further comprising: an inter-layerdielectric (ILD) over the STI region, wherein the metal pad furtherextends into the ILD, and wherein edges of a portion of the metal pad inthe ILD are substantially aligned to respective edges of a portion ofthe metal pad in the STI region.
 12. The circuit structure of claim 11,wherein the interface extends from the top surface of the semiconductorsubstrate into the semiconductor substrate.
 13. The circuit structure ofclaim 10, wherein the STI region and the metal pad have circular-shapededges.
 14. The circuit structure of claim 10 further comprising: anadditional STI region, wherein both the STI region and the additionalSTI region extend from the top surface of the semiconductor substrate tostop at a same intermediate level between the top surface and the backsurface of the semiconductor substrate; and a transistor comprising asource/drain region having a sidewall contacting a sidewall of theadditional STI region.
 15. A circuit structure comprising: asemiconductor substrate; a first shallow trench isolation (STI) regionand a second STI region extending from a top surface of thesemiconductor substrate into the semiconductor substrate, with bottomsurfaces of both the first STI region and the second STI region at asame intermediate level between a top surface and a bottom surface ofthe semiconductor substrate; a transistor comprising a source/drainregion having a sidewall contacting a sidewall of the second STI region;a metal pad extending from a level higher than a top surface of thefirst STI region into a center portion the first STI region, with anouter portion of the first STI region forming a ring encircling themetal pad; and a through-substrate via (TSV) extending from a backsurface of the semiconductor substrate to contact a bottom surface ofthe metal pad.
 16. The circuit structure of claim 15, wherein the outerportion comprises an inner edge in physical contact an edge of the metalpad to form an interface, and the interface forms a full ring.
 17. Thecircuit structure of claim 15, wherein the first STI region and thesecond STI region are formed of a same dielectric material.